In college I took a graphics arts class for fun and applied my engineering skills to it. In two cut paper projects, I applied mathematics to design shapes that looked correct when viewed straight-on, but were actually fairly large three-dimensional structures.
This technique was a lot of fun; in fact the second project required a computer program to calculate the dimensions of all the paper items I had to cut out.
Recently a friend of mine sent me a link to a similar technique applied to a more massive scale: Messing with the Optical Mind. This looks like something really cool to do with a boring hallway in your house, although I think I would use less dramatic colors.
